The plumbing industry has long recognized the benefits which are derived by employing a trap between a source of refuse liquid and a conduit to a sewer or holding system. Such traps are commonly found running, for example, from the tail pipe of a sink to a drain pipe which may empty into a sewerage system.
A conventional trap is generally tubular, fabricated of metal or synthetic plastic, and comprises a U-bend. The inlet leg of the U, that is the leg which may connect to a tail pipe, leading from, for example, a sink, is usually longer than the outlet leg of the U giving the trap configuration a J-shape. The union between the trap and the downstream member is accomplished usually by fabricating the trap member with male threads and providing a female threaded fastening means which engages a flange or bead on the other member so that the fastening of the female threaded means to the male threads, in place, with a rubber seal, if necessary, provides a generally leak-proof union.
The tail pipe engages the trap inlet (upstream) opening and generally fits into the opening a short distance. The inlet opening comprises a threaded annular rim which co-acts with a compression ring which holds the tail pipe securely in place when pressure is applied by tightening a tail pipe-encompassing fastening means against the ring.
In use, the plumbing trap serves the purpose of not only inter-connecting a pipe leading from a source of refuse liquid to a drain pipe, but acts as an odor and vapor barrier when liquid is not being conducted therethrough. The lowermost portion of a trap comprises the U-bend, the inlet and outlet openings being located thereabove. Accordingly, water running into the trap from a tail pipe falls to the lowest point in the trap, the U-bend, before running up to the drain pipe inlet. Stimulus for movement of the liquid in this fashion is the head of liquid in the tail pipe and inlet arm of the trap. When liquid ceases to enter the tail pipe and trap inlet arm, the liquid in the U-bend equilibrates and fills the U-bend with standing liquid which prevents fumes and odors from passing from the drain pipe to the tail pipe and into the ambient environment.
One improvement in the joining surfaces between a synthetic plastic trap and a downstream member (drain pipe) which is known, comprises the double seal design downstream trap opening. In this design the outlet opening of the trap comprises an annular rim which has twin surfaces capable of mating with complimentary surfaces of a downstream member, thereby providing the double seal. This design, however, has significant drawbacks.
In particular, due to fabrication problems, the threaded portion of the double seal end of the trap was never made the same threaded diameter as the threaded upstream end. This required different diameter fastening means for each end of the trap and did not permit the trap to be used with, for example, a conventional brass downstream member due to the oversized nature of the downstream threaded end of the trap and concomitant oversized nature of the double seal surfaces.
British Patent Specification No. 487,796, accepted June 24, 1938, ussued to Mott, is the first description of a double seal configuration in a conduit union. Mott uses the double seal union in a pressurized beer distribution system. The double seal terminal is soldered or screwed to the conduit and in no sense can the device of Mott be considered a continuous structure. Mott neither teaches the use of the double seal connection in non-pressurized situations nor does he anticipate incorporating a J- or U-configuration into his conduit tubing. Such a configuration would obviously serve no purpose in the Mott device.
U.S. Pat. No. 3,719,209, issued Mar. 6, 1973, to Rush et al. claims a tubular trap formed by a particular blow molding technique which comprises:
(1) extruding a parison of molten plastic and clamping it between die members having the configuration of the extended shape of the article to be molded (Rush et al., FIG. 4); PA1 (2) introducing blow-molding ducts into the die members and parison to assist in forming the article configuration and provide air under pressure to force the parison against the sides of the mold until the plastic has cooled (Rush et al., FIG. 3); and PA1 (3) parting the die members and stripping the molded article from the mold.
Rush's et al. contribution to technology did not lie in the particular configuration molded, but in the step of using positive pressure to conform the parison walls to the die configuration. As a matter of fact Rush's et al. claims are couched in product by process format. It will be apparent from the configuration of the trap claimed herein that it could not be fabricated by the Rush et al. method since the falling parison technique cannot be utilized to form the double seal configuration on the downstream end of the trap of the present invention (see, for example, FIG. 8 of Rush et al.).